Various types of stuffing boxes are commercially available for placing on a wellhead to seal with the rod string to power a downhole pump. In some applications, the rod string is reciprocated in the well to power the downhole pump, and the stuffing box is designed to seal with the rod string while accommodating that reciprocation. In other applications, such as those involving a progressive cavity pump, the rod is rotated in the well, and the stuffing box then is intended to seal with the rotating rod string which powers the downhole pump, and most importantly does not wear or otherwise damage the rod string, which may lead to failure.
U.S. Pat. No. 5,823,541 discloses a rod seal cartridge for a progressive cavity pump with a single o-ring seal between the rod and the sleeve. U.S. Pat. No. 6,843,313 discloses a stuffing box with fluid pressure energized static seals between the rod and the sleeve, and packings between the housing and the sleeve to provide a dynamic seal. U.S. Pat. No. 7,044,217 discloses a similar arrangement, with a coil spring acting on the dynamic seals. Canadian Patent 2,095,937 also discloses static seals between the rod string and an extension of a sleeve, with seal cartridges between the sleeve and the housing.
The disadvantage of the prior art is overcome by the present invention, an improved stuffing box and method of sealing with the rod string are hereinafter disclosed.